by Alan M. Kapuler Ph.D. May 1, 2000
It took three visits to Baja California, the long and narrow peninsula of land that is the southernmost tip of land of Turtle Island, the northamerican continent that I sometimes call my home, before I realized what was wrong. The thorny plants that inhabit the dry climate are very beautiful and are generally rare in the perspective of the world flora. Surprisingly, the native flora of this tropical desert ecosystem is on the verge of massive extinction.
Several converging and nested forces have led to this remarkable circumstance. For more than 50 years, large numbers of free range cattle and goats have eaten almost all the young plants of a wide variety of species, genera and families. The open and unrestricted grazing habit of these herbivores has reduced or eliminated populations of young cacti, daisies, mints, burseras, morning glories, figs, cucurbits, scrophularias, phlox, and in particular and perhaps most important, legumes. Legumes in the desert tropics belong to three major groups, reckoned by botanists as either families or subfamilies. These are the Caesalpiniaceae which includes the cassias, carob, sennas, orchid trees, redbuds, cercidiums, tamarind...; the Mimosaceae which includes acacias, desmanthus, prosopis, calliandras, lysilomas, icecream beans ....and the Fabaceae which includes .....31 tribes (see Peace Seeds Resource Journal1994 7: 31-40). The published flora of Baja California (Wiggins The Flora of Baja California, Stanford University Press 1980) gives 10 genera and 31 species for the Caesalpiniaceae, 11 genera and 39 species for the Mimosaceae and 38 genera and 153 species for the Fabaceae. The flora contains some 2700 species, of which about 18% are legumes. There are actually no young plants of these legumes that we could find in weeks of walking through various parts of the southern Baja region. Within fenced domains where the herbivores are kept out, there are occasional young legume plants. However, since water is a scarce and precious resource, and since there have been only inches of rain during the past two years, few legumes germinate and grow even in these protected environments. Occasional succulent plants survive in the shelter of the very spiny and recumbent cacti (Creeping Devils, Lemaireocereus eruca and L. gummosus ) but these were never legumes, just other not quite so spiny kinds.
Why are the legumes so important. There are several reasons.1. They provide mottled shade for young plants of many families. Once the young are established they can outgrow their legume nurses that have protected them from the intense and dessicating sun.2. Nursing by legumes is done not only by providing shade, but by their ability to fix nitrogen on their roots by providing cellular structures that are housing for rhizobial bacteria. These useful microbes increase the fertility of the soil and provide nutrients essential for the growth of many other kinds of plants such as grasses and daisies.3. Legumes provide nectar and pollen for bees, flies, wasps and other pollinators. By sheltering other kinds of plants that also provide nectar, pollen and shelter for a host of other pollinators, the legumes are primary in ensuring pollination and hence seed set for many, many kinds of plants. So, when the legumes are extincted by grazing, so are the pollinators and the difficulty in rebuilding the ecosystem is compounded. Furthermore, since seed supplies in a broad range of plants is reduced and eliminated, the mammals and birds that eat them are also diminished and hence the carnivores also are reduced in numbers. Thus the whole ecosystem of organisms, the web of life is threatened, reduced and destroyed. The legumes are the third largest group of plants, following the orchids and the daisies. There are about 659 genera and 16729 species. I estimate that about 80% of these grow in sub-tropical and tropical conditions. Of these perhaps half are from desert ecosystems. So about 7000 species are under stress from overgrazing. Thus the basic sustaining force of diversity in the tropical desert ecosystems, the legumes, which are the core of the fertility and vitality for the entire multidiversity of organisms are being wiped out. For this major group of plants to have incipient extinction throughout its natural domain is an ecological crisis of unprecedented magnitude. That it ramifies throughout the interconnected living food web impacting mammals and birds is a ongoing consequence.
What I saw is an age stratified society with a disproportionately large population of aged plants, stark in their increasingly sterile isolation. The magnificent cardon, Pachycereus pinglei, a giant cactus, close relative of the sahuaro (Carnegia gigantea ) that grows in the SW USA deserts, tipifies the local Baja landscape with huge trunks, a few giant branches, white flowers 20 feet above my head, pecked out and hollowed nests for owls, and no young ones. Once the notion that there were no young presented itself, I began looking for young cardon. After three weeks and no young, I asked a local farmer who had lived all 46 years if his life in the bioregion if he had ever seen a young cardon. "No, senor". Estimates of the age of the majestic old cacti is from 200-500 years old. Walking down a river of crystalline white quartz sand in a wash running between low rounded hills of red clay impregnated with rocks of all sizes, there were huge stocky-trunked twisted-limb legumes of several genera and species (Cercidium, Parkinsonia, Pithecellobium, Acacia, Prosopis). Some were awe-inspiring massive trees that have provided shelter for many kinds of creatures for hundreds of years. Like the cardon cacti, there were no young plants of these legume species. Estimates of the age of the remaining old trees is 200-400 years old.
Of many species, even the older plants are scarce. What are we to do? Collect seeds of the remaining species. Focus on legumes, include as many other kinds as possible. Plant the seeds and bring up new generations of a wide diversity of plant kinds that can inhabit the tropical desert ecosystems. Fence out herbivores and plant legumes. Introduce new young plants of the ancients that have been the core of the sustainable flora. Collect eco-overlapping genera and species on a world basis to broaden the base of conservation. Plant kinship gardens to provide educational and living germplasm resources for the current and future generations. Nourish the return of the pollinators and the reestablishment of the complex web of organisms that provides and living and viable future for all life. Practice sustainable organic agriculture and species hyperdensification in caretaking the biosphere. Ecosanity.
Dr Kapuler is Seed Breeding Consultant to Sow Organic Seed Company www.organicseed.com"
No comments:
Post a Comment